Up north, where I'm from, I'm usually straight to the point. I don't want to pay for a massage and not get anything extra.
If you're in central London, and are pushed for time, but really need to get your end away, the best thing to do is get down to Soho and visit a walk-up, you can be in and out (pun intended) in a as little as 15 minutes.
With Thai and Chinese massage shops, you've really got to play the game.
Myself, I don't ask about extras until "the turn"...

Going into a shop and asking the front man/woman about extras is not playing the game. Remember many Thai girls do not see themselves as sex workers.
You could have been a copper, an immigration official, a local authority officer or a newspaper reporter.
These days, raids, are euphemistically called "welfare visits"... these are either carried out by just the Police, or a multi agency team. If the person at the front desk had addmited that extras were on the menu, he/she would be running the risk, you would then call up the rest of your team and turn the place over, under the guise of a welfare check on the girls.
Having said all of the above, I have heard of customers negotiating an extras deal at the front desk, but only out in the sticks.
P.S. Don't go to Brixton and ask the first black guy you see, if he's got any drugs..